1. Field of the Invention
The present invention relates to a liquid crystal display and a method of manufacturing the same, and is applicable to various liquid crystal modes such as TN (Twisted Nematic), ECB (Electrically Controlled Birefringence), STN (Super Twisted Nematic), IPS (In-Plane Switching), FFS (Fringe Field Switching), etc. According to the present invention, the surface on the lower side of an orientation film is formed in a grooved shape to provide the orientation film with an orienting ability in a specified direction, thereby realizing a higher productivity, a more satisfactory orientation control force for a liquid crystal, and a higher image quality, as compared to those obtained according to the related art.
2. Description of the Related Art
In the past, in liquid crystal display panels of various liquid crystal modes such as TN, ECB, STN, IPS, FFS, etc., the liquid crystal molecules are oriented in a fixed direction by an orienting treatment, and a variety of techniques have been proposed for carrying out the orienting treatment.
The rubbing method as one of the orienting treatments is the most frequently used method, in which an orientation film composed of a film of a polymer such as a polyimide is formed on a transparent electrode, and thereafter the orientation film is rubbed in a fixed direction by a roller fitted with a cloth or the like on the surface thereof, whereby an orienting ability is imparted to the orientation film. The rubbing method, however, has the problem that the surface of the orientation film may be stained by deposition of debris generated upon rubbing, and that the TFTs (Thin Film Transistors) on the panel may be broken due to generation of static electricity.
The so-called grating method as an orienting treatment method substituting for the rubbing method is a method in which the surface of a substrate is processed to form a grating (grooves), and the elastic strain arising from the grating is utilized to orient the molecules of a liquid crystal. In the grating method, the liquid crystal molecules are oriented in the direction parallel to the grating in which the elastic free energy is most stabilized.
In relation to the grating method, M. Nakamura et al., J. Appl. Phys., 52, 210 (1981) proposes a method in which a photosensitive polymer layer is irradiated with light to form a grating in the form of straight lines arranged at a fixed interval. In addition, Japanese Patent Laid-open No. Hei 11-218763 proposes a method in which a photo-polymerizable monomer on a substrate is irradiated with light to form a grating-formed orientation film. Besides, Japanese Patent Laid-open No. 2000-105380 proposes a method in which by application of a technique of transfer, a resin coating film on a substrate surface is provided with a grating-like recess-and-protuberance (undulating) shape, to thereby form a grating-formed orientation film.
In the grating method, it is known that the anchoring energy can be controlled by regulating the pitch and height of the grating (Y. Ohta et al., J. J. Appl. Phys., 43, 4310 (2004)).
In relation to the grating method, besides, there has been proposed a method in which the anchoring strength is enhanced by utilizing the orientation control force possessed by the orientation film material (such as polyimide) itself. Specifically, Japanese Patent Laid-open No. Hei 5-88177 proposes a method in which a photosensitive polyimide is patterned by photolithography, and Japanese Patent Laid-open No. Hei 8-114804 proposes a method in which the surface of a first orientation film is provided with a recess-and-protuberance shape which is stripe-shaped in a predetermined direction and which has a saw-toothed surface profile in the direction orthogonal to the predetermined direction, and an organic matter with molecular axes oriented in the orthogonal direction is layered on the first orientation film to form an orientation film. Further, Japanese Patent Laid-open No. Hei 3-209220 proposes a method in which a photosensitive glass is photo-etched to form the glass surface into a recess-and-protuberance shape, followed by applying an orientation film material to the thus shaped surface.
According to the grating method, it is possible to obviate the staining of the orientation film surface and the generation of static electricity which are frequently encountered in the rubbing method.